fangpeina opened a new pull request, #3379:
URL: https://github.com/apache/nuttx-apps/pull/3379
## Summary
This PR implements stderr redirection support in NSH (NuttShell), enabling
Bash-like syntax for redirecting standard error output. This enhancement
improves NSH compatibility with standard Unix shells and provides better error
handling capabilities.
### Features Added:
- Support `2>` operator for stderr redirection (overwrite mode)
- Support `2>>` operator for stderr redirection (append mode)
- Support `2>&1` syntax to redirect stderr to stdout
- Works with both foreground and background commands
### Usage Examples:
```bash
nsh> ls noexists 2> err.log # Redirect stderr to file
nsh> ls noexists 2> err.log & # Background with stderr redirect
nsh> ls noexists 2>> err.log # Append stderr to file
nsh> sh < /dev/ttyS0 > /dev/ttyS0 2> /dev/ttyS1 & # Multiple redirections
nsh> sh < /dev/ttyS0 > /dev/ttyS0 2>&1 & # Merge stderr to stdout
```
### Implementation Details:
- Added stderr file descriptor field to `nsh_vtbl_s` structure
- Extended redirection parsing logic in `nsh_parse.c` to handle stderr
operators
- Implemented `nsh_redirect_stderr()` function in `nsh_fileapps.c`
- Updated console and script handlers to support stderr redirection
## Impact
- **Features**: Adds stderr redirection capability to NSH shell, enhancing
compatibility with standard Unix shell syntax
- **API Changes**: Modified `nsh_vtbl_s` structure to include stderr file
descriptor (internal API only, no user-facing changes)
- **User Experience**: Users can now redirect error messages separately from
standard output, improving script debugging and error logging
- **Build**: No build system changes required
- **Hardware**: No hardware-specific dependencies, works on all platforms
- **Documentation**: No documentation updates required (standard shell
feature)
- **Security**: No security implications
- **Compatibility**: Fully backward compatible - existing NSH commands and
scripts continue to work unchanged
## Testing
### Test Configuration:
- **Platform**: QEMU simulation (sim:nsh)
- **Architecture**: Host architecture via NuttX simulator
- **Config**: sim:nsh
### Runtime Test Results:
**Test 1: Basic stderr redirection (overwrite mode)**
```bash
nsh> ll 2> err.log
nsh> cat err.log
nsh: ll: command not found
```
**Test 2: Stderr append mode**
```bash
nsh> ll 2> err.log
nsh> cat err.log
nsh: ll: command not found
nsh> ls noexists 2>> err.log
nsh> cat err.log
nsh: ll: command not found
nsh: ls: stat failed: 2
```
**Test 3: Multiple append operations**
```bash
nsh> ls noexists 2> err.log
nsh> cat err.log
nsh: ls: stat failed: 2
nsh> ls file1 2>> err.log
nsh> cat err.log
nsh: ls: stat failed: 2
nsh: ls: stat failed: 2
```
**Test 4: Redirect stderr to stdout (2>&1)**
```bash
nsh> ls > log 2>&1
nsh> cat log
/:
bin/
data/
dev/
err.log
etc/
log
proc/
tmp/
```
### Hardware Platforms Tested:
- [x] NuttX simulator (sim:nsh configuration)
- [ ] Physical hardware (not required for shell feature testing)
### Code Style Check:
```bash
$ /home/fpn/disk/github/nuttx/tools/checkpatch.sh -g HEAD~
✔️ All checks pass.
```
## Documentation
N/A - This implements standard Unix shell stderr redirection syntax that is
well-documented in general shell documentation.
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